1. Field of the Invention
The present invention relates to a fuel supply system of an engine for an automobile, etc.
2. Description of the Prior Art
In order to obtain better ignition and higher efficiency of combustion, it is desirable that fuel which is supplied to an engine is preheated up to a proper temperature. Needless to say, preheating of fuel is much more desirable in an engine of an automobile, etc., which is operated in a cold environment. However, if fuel is heated excessively in a tube which extends from a fuel pump to a carburetor or a fuel injection device, there is a danger that vapour lock will occur in the tube, causing interruption of fuel supply. In order to preheat fuel supplied to an engine up to a predetermined temperature, the usual practice is to employ an electric heater equipped with temperature control means. However, since a common electric heater controlled by a thermostat or the like generally operates with relatively wide fluctuations in the controlled temperature and, in addition, the flow of fuel which passes through the heater violently changes according to operating condition of an automobile, it is very difficult to maintain a constant predetermined preheating temperature of the fuel which reaches a carburetor or a fuel injection device.